Another way to do that while claiming dual boot Linux ready to use:
Create an Android app that when clicked on checks to make sure that there is a microSDXC card in the Gemini, asks the user if it's OK to overwrite it then if Yes to both, downloads and writes the Debian Linux image directly to the microSDXC.
Then they'd pretty well have to ship the SD card with the unit, because otherwise they'd have to say not that it ships dual boot but that when it ships dual boot would be possible with the addition of non-included storage. In short, the whole dual-booting Linux thing would be a lie. If additional storage is required to run Linux, they surely would have said so by now.
I've seen that idea floated around a few times - that the unit will ship with both Android and Linux pre-installed on the eMMC. However, I have not seen anything from Planet Computers that directly claims that.
What the Indiegogo listing for the Gemini says about Linux:
"Designed for Android, it also features a dual boot Linux option"
"What Linux distribution will Gemini run?
We are currently talking to a few companies representing different Linux flavours and we are considering a number of options but the decision has not been taken yet. We are also taking into accounts comments from the backers into consideration, including Sailfish & Ubuntu OS, which have been suggested several times."
That is all. "Dual boot Linux option" does not equal, "Linux pre-installed."
Note this video showing the Gemini booting Linux:
https://vimeo.com/239095559At 16 seconds into the video you see that in order to boot Linux, the side-button must be held until the logo splash screen appears.
If this were truly dual boot from the eMMC, then it should boot to a bootloader selection menu drawn from the eMMC.
The key hold during power on is critical to this assessment - it's happening prior to and through the device reset. I.e. it appears to be a conditional choice during boot media selection. Pretty much every phone I've encountered with a microSD card slot has a 'secret button' combination that when held during reset points the device to boot from microSD.
If it were 'Two OS installs on one eMMC' dual boot, then there would have to be a select write to the bootloader when exiting Android to tell it to boot Linux when it restarts. I.e. something on the eMMC's bootloader to tell it to go to the next partition.
We'll see, but I will not only not be surprised but very happy if this is booting Linux from the microSD (at the end user's option) and leaving the eMMC to Android. And yes, I plan to use both. I simply prefer to keep the two separated with Debian Linux on a media point that is easily backed up, changed out, changeable, etc...